1. Field of the Invention
The present invention relates to novel compounds, heteroarylcarboxylic acid ester derivatives, which exhibit a serine protease (particularly trypsin and enteropeptidase) inhibitory activity. The present invention also relates to pharmaceutical compositions which contain such a compound and drugs for the treatment or prophylaxis of diabetes. The present invention further relates to methods for the treatment and/or prophylaxis of diabetes by administering such a heteroarylcarboxylic acid ester derivative.
2. Discussion of the Background
At present, insulin secretagogues (sulfonylureas), glucose absorption inhibitors (α-glucosidase inhibitors), insulin sensitizers (biguanide, thiazolidine derivatives), and the like are clinically used as therapeutic drugs for diabetes. However, since all of them are accompanied by side effects such as hypoglycemia, diarrhea, lactic acidosis, edema, and the like; show an insufficient effect; and the like, a medicament satisfying clinical needs is still needed.
In recent years, a benzoic acid ester having a protease inhibitory activity, which is represented by the following compound, has been reported to show a blood glucose elevation suppressing action in a diabetes animal model (see WO2006/057152, which is incorporated herein by reference in its entirety). The following compound is considered to show an enzyme inhibitory activity on trypsin, thrombin, pancreatic, and plasma kallikreins, plasmin and the like and a leukotriene receptor antagonistic action. Moreover, an enteropeptidase inhibitory activity of the following compound has also been reported (see Biomedical Research (2001), 22 (5) 257-260, which is incorporated herein by reference in its entirety). However, many unclear points remain in the relationship between such actions and a blood glucose elevation suppressing action.

On the other hand, as for a heteroarylcarboxylic acid ester structures, JP-A-55-161385, which is incorporated herein by reference in its entirety, discloses a compound as a therapeutic drug for pancreatitis. In this document, only heteroarylcarboxylic acid ester compounds wherein the substituent of the heteroarylcarboxylic acid moiety is a methyl group or a methoxy group or unsubstituted compounds are disclosed, as represented by the following formula. While these compounds are disclosed as showing an inhibitory activity on trypsin, chymotrypsin and thrombin, no description is given as to the enteropeptidase inhibitory activity and blood glucose elevation suppressing action.

In addition, Advances in Experimental Medicine and Biology (1989), 247B (Kinins 5, Pt. B), 271-6, which is incorporated herein by reference in its entirety, also describes a heteroarylcarboxylic acid ester having a protease inhibitory activity, which is represented by the following formula. However, only compounds wherein the heteroaryl moiety is unsubstituted are disclosed, and no description is given as to the enteropeptidase inhibitory activity and blood glucose elevation suppressing action of these compounds.

Furthermore, WO99/41231, which is incorporated herein by reference in its entirety, describes a compound represented by the following formula. However, it has a structure wherein an aryl group substituted by a carboxyl group is directly bonded to the heteroaryl moiety, which is completely different from the compound of the present invention. The document discloses an inhibitory activity against blood coagulation factor VIIa; however, no description is given as to the enteropeptidase inhibitory activity and blood glucose elevation suppressing action.

On the other hand, trypsin is one of the intestinal serine proteases and is produced by degradation of inactive trypsinogen by enteropeptidase. Trypsin is known to activate various digestive enzymes by acting on chymotrypsinogen, proelastase, procarboxylesterase, procolipase and pro-sucrase-isomaltase, and the like. Therefore, it is considered that an inhibitor of enteropeptidase and trypsin lowers the digestive capacity for protein, lipid, and carbohydrates, and is effective as a drug for the treatment or prophylaxis of obesity and hyperlipidemia.
WO2006/050999, which is incorporated herein by reference in its entirety, describes that a medicament that inhibits both enteropeptidase and trypsin is interesting as a body fat-reducing agent. In addition, WO2009/071601, which is incorporated herein by reference in its entirety reports a compound which has an inhibitory activity against enteropeptidase, trypsin, plasmin, kallikrein, and the like as an antiobesity drug. However, neither of these publications describes suppression of blood glucose elevation and hypoglycemic effect afforded by simultaneous inhibition of enteropeptidase and trypsin, and the protease inhibitor described therein has a structure completely different from that of the compound of the present invention.
Accordingly, there remains a need for compounds which are useful for the treatment or prophylaxis of diabetes. Therefore, to further satisfy the clinical needs from the aspects of effect, safety and the like, a hyperglycemic inhibitor having a serine protease inhibitory action, which is a new drug for the treatment or prophylaxis of diabetes, is desired.